The present invention relates to a defect inspection method and apparatus to be same used for inspection of patterns and contaminants in which an inspected pattern is examined for defects (short-circuits and line breaks), especially in semiconductor wafers, liquid crystal displays, and photomasks. In the following description, defects will be considered to include contaminants.
Conventionally, as described in Japanese laid-open patent publication number Hei 7-318326 (background technology 1), in this type of inspection device, the inspected pattern is moved while using an imaging element such as a line sensor, to detect an image of the inspected pattern. The detected image signal is compared to the concentrations in an image signal delayed by a predetermined interval, and discrepancies are recognized as defects.
Another conventional technology relating to defect inspection of inspected patterns is presented in Japanese laid-open patent publication number Hei 8-320294 (background technology 2). In this background technology 2, the inspected pattern is a semiconductor wafer or the like in which a chip contains both areas with high pattern densities, such as memory arrays, and areas with low pattern densities, such as peripheral circuitry. The frequency distribution of the brightness of the detected image is used to apply tone conversion to the digital image signal obtained from AID conversion of the detected image signal. This tone conversion is performed so that there is a predetermined relationship between the brightnesses or contrasts of the high-density areas and the low-density areas on the inspected pattern. This tone-converted image signal is aligned with an image signal that has been tone converted for comparison. The two images are compared to perform high-precision inspection of fine defects.
Furthermore, a device for inspecting photomask patterns is presented in Japanese laid-open patent publication number Hei 10-78668 (background technology 3). In this device, a UV laser, such as an excimer laser, is used as a light source. A diffuser panel inserted in the light path is rotated to reduce the coherence of the UV light, allowing a uniform UV illumination to be applied to the mask. Characteristics are calculated from the resulting mask image data, and these characteristics are used to evaluate the quality of the photomask.
In recent years, LSI production has involved higher degrees of fineness in the circuit patterns formed on wafers to respond to the demand for higher densities of integration. Pattern widths of 0.25 microns and less are being used, reaching the limits of the resolutions provided by imaging optical systems. For this reason, the use of high-NA imaging optical systems and super-resolution technology is being developed.
However, high-NA imaging has reached physical limitations. Thus, the essential approach involves shortening the wavelength used for detection from UV to DUV.
Also, since inspection must be performed at high speeds, it is not possible to have a tightly focused laser beam scanning the specimen. If, on the other hand, a laser beam is spread out to cover the entire viewing area, specking will take place. There will also be over-shooting and under-shooting, known as linking, at the edges of the circuit pattern. These issues prevent good images from being obtained.
The object of the present invention is to overcome the problems described above and to provide a defect inspecting method and apparatus that performs high-speed, high-resolution detection of fine circuit patterns.
In order to achieve this object, the present invention uses a light source that emits UV light as the light source for the inspecting device. More specifically, in the embodiments of the present invention, a UV laser light source is used as the light source. Means for restricting speckling of the UV laser is disposed in the optical path. Coherence of the UV light is reduced and the UV light is illuminated on the surface of the inspected item so that an image of the inspected item can be detected. UV light in this case can include DUV light.
In accordance with the present invention, this means for restricting speckling in the UV light can involve: 1) focusing the light from the light source onto one or multiple points on the pupil of the objective lens, and scanning the focused points over the pupil with a timing based on the storage time of the detector; 2) projecting the UV light emitted from the laser light source into a bundle of optical fibers with optical axis offsets and focusing the exiting lights onto the pupil of the objective lens; 3) projecting the light into a set of optical fibers having optical path lengths at or greater than the coherence length of the laser light source, and focusing the exiting light onto the pupil of the objective lens; 4) providing a diffuser panel and moving it relative to the light beam in a direction-roughly perpendicular to the optical axis; 5) illuminating the pupil using a combination of the above methods; and the like.
Also, in order to enhance pattern contrast, the ability to freely control the polarization of the laser was studied. By controlling the orientation of the polarization and ellipticity of the illuminating light, partial polarized components in the detected light can be detected.
In order to achieve the objects described above, the present invention provides a pattern defect inspecting device including: laser light source means emitting a laser beam; means for reducing coherence of the laser beam emitted by the laser light source means; means for illuminating a specimen with a laser beam having coherence reduced by the coherence reducing means; means for detecting an image of the specimen illuminated by the laser beam produced from the illuminating means; and means for detecting pattern defects formed on the specimen based on information relating to the image of the specimen detected by the image detecting means.
In order to achieve the objects described above, another aspect of the present invention provides a pattern defect inspecting device including: laser light source means emitting a UV laser beam; means for reducing coherence of the UV laser beam emitted by laser light source means; means for illuminating a specimen with a UV laser beam having its coherence reduced by the coherence reducing means; means for changing polarization of the UV laser beam; means for detecting an image of the specimen illuminated by the UV laser beam provided from the illuminating means and polarized by the polarizing means; and means for detecting pattern defects formed on the specimen based on information relating to the image of the specimen detected by the image detecting means. In order to achieve the objects described above, another aspect of the present invention provides a pat tern defect inspecting device including: laser light source means emitting a laser beam; means for reducing coherence of the laser beam emitted by laser light source means; means for illuminating a specimen with a laser beam having its coherence reduced by the coherence reducing means; means for detecting an image of the specimen illuminated by the laser beam produced from the illuminating means; and means for processing an image of the specimen detected by the image detecting means. A wafer with a diameter on the order of 200 mm is processed at a speed corresponding to a throughput of three units per hour, and defects of 100 nm can be detected on the patterns formed on the specimen.
In order to achieve the objects described above, another aspect of the present invention provides a pattern defect inspecting method including the steps of: illuminating with al UV laser a specimen on which a pattern is formed; imaging the specimen illuminated with the UV laser; and detecting defects on the pattern by comparing an image of the specimen obtained by the imaging step with a previously stored reference image.
In order to achieve the objects described above, another aspect of the present invention provides a pattern defect inspecting method including the steps of: focusing and scanning a UV laser beam on a pupil of an objective lens; illuminating a specimen on which a pattern is formed with the focused and scanned UV laser beam; imaging the specimen illuminated by the UV laser beam; and detecting defects on the pattern by comparing an image of the specimen obtained by the imaging step with a previously stored reference image.
In order to achieve the objects described above, another aspect of the present invention provides a pattern defect inspecting method including the steps of illuminating a specimen on which a pattern is formed with UV light; imaging the specimen illuminated by UV light; correcting image brightness for an image of the specimen obtained by the imaging step and a previously stored reference image so that the brightnesses are roughly identical; and detecting defects on the pattern by comparing the image of the specimen and the reference image which have been corrected for brightness.
In order to achieve the objects described above, another aspect of the present invention provides a pattern defect inspecting method including the steps of: reducing the coherence of a laser beam emitted from a laser light source; illuminating a surface of a specimen on which a pattern is formed via an objective lens using the laser beam with reduced coherence while varying the direction of illumination over time; imaging the specimen illuminated by the laser beam; and detecting defects on the pattern by comparing the image of the specimen obtained in the imaging step and a previously stored reference image.
In order to achieve the objects described above, another aspect of the present invention provides a pattern defect inspecting method including the steps of: illuminating a surface of a specimen using UV light; obtaining an image signal by imaging the surface of the specimen illuminated by the UV light; detecting defects of 100 nm and less on the specimen by processing the image signal; and outputting information relating to positions on the specimen of detected defects of 100 nm and less.
In order to achieve the objects described above, another aspect of the present invention provides a pattern defect inspecting method including the steps of: illuminating UV light on a wafer with a diameter that is at least on the order of 200 mm; detecting an image of the wafer by imaging the wafer illuminated by the UV light; detecting defects 100 nm and less on patterns formed on the wafer by processing the detected images of the wafer illuminated by the UV light, the detection being performed at a throughput of at least three wafers with 200 mm diameter per hour.